This invention relates to a tank and a method for making the tank.
FIGS. 1 through 4 show a conventional tank and a conventional machine for making such a tank. An upper shell 1 of a tank has a flange 1a. A lower shell 2 also has a flange 2a. The flange 1a of the upper shell 1 and the flange 2a of the lower shell 2 must be matched when they are seam-welded at the whole periphery thereof. In practice, the flanges 1a and 2a are provisionally spot-welded at a selected portion thereof as shown by the numeral 3 in FIG. 2 in order to avoid the displacement of the flanges 1a and 2a. After the flanges 1a and 2a are spot-welded to form a tank W, the upper shell 1 and the lower shell 2 are together set in a work receiver 6 of a seam welding machine 5 (FIG. 3).
As shown in FIG. 3, the work receiver 6 is fixed to a profiling cam 9 which in turn is rotatably supported by a shaft 8 of a holding frame 7 (FIG. 4). An upper pad 10 is also attached to the holding frame 7 in coaxial relation to the shaft 8. The tank W is rotatably pressed by the upper pad 10 toward the work receiver 6. A roller 11 is rotatable and positioned always at the same place. The profiling cam 9 is pressed between a guide plate 12 and the roller 11. A pair of roller electrodes 13 press therebetween the flanges 1a and 2a of the tank W as shown in FIG. 3 so as to weld the flanges 1a and 2a. The roller electrodes 13 are driven by a pair of driving members 14.
The outer profile of the profiling cam 9 exactly corresponds to the seam-welding locus of the flanges 1a, 2a.
A contact point between the profiling cam 9 and the guide plate 12 is positioned in a straight line X (FIG. 4) which passes the center of the roller electrodes 13.
In operation, the roller electrodes 13 are driven by the driving members 14 so that the flanges 1a and 2a of the tank W pressed between the pair of roller electrodes 13 are welded to each other at a pressing point of the roller electrodes 13. For instance, if the flanges 1a and 2a are fed in the direction of the arrow A, the profiling cam 9 moves in the same direction because the work receiver 6 supporting the tank W is fixed to the profiling cam 9. The movement of the profiling cam 9 is controlled by the roller 11 and the guide plate 12. Therefore, the locus of the welded portion or the seam welding line of the flanges 1a and 2a follows the cam shape of the profiling cam 9 by way of the work receiver 6.
The holding frame 7 can move laterally in response to the movement of the profiling cam 9 together with the tank W, the work receiver 6 and the profiling cam 9 supported thereby between the shaft 8 and the upper pad 10.
However, in such conventional tanks as above-mentioned, before the flange 1a of the upper shell 1 is matched with the flange 2a of the lower shell 2 for the seam welding purpose, some part of the flanges 1a and 2a must be spot-welded in order to avoid the displacement thereof. In other words, a spot welding step must be added to a seam welding step according to a conventional method for making a tank.